Teletherapy head having shielding carrier for radioactive source



May 1, 1962 R. v. WOLF 3,032,661

TELETHERAPY HEAD HAVING SHIELDING CARRIER FOR RADIOACTIVE SOURCE FiledMarch 4, 1957 2 Sheets-Sheet 1 FIG. l xx 39 e 59 T d 64 60 f/ g 4& '7 43'.l

22 l3 14 FIG. 2 f 23 i4 25 INVENTOR.

ERT

5'" ATTORNEY May 1, 1962 R. v. WOLF 3,032,661

TELETHERAPY HEAD HAVING SHIELDING CARRIER 5 FOR RADIOACTIVE SOURCE-Filed March 4, 1957 2 Sheets-Sheet 2 22 23 FIG. 3

45 47 4s 47 4a 24 25 d FIG. 6 FIG. 4 FIG. 7

44 INVENTOR.

44 R RT V. WOLF Iijlfia BY Kg FIG. 5

4 2 43 46 42,43 ATTORNEY United States Patent 1 3,032,661 ,TELETHERAPYHEAD HAVING SHIELDING CARRIER FOR RADIOACTIVE SOURCE Robert V. Wolf,Webster Groves, Mo., assignor to Nilclear Corporation of America, Inc.,New York, N.Y., a corporation of Michigan Filed Mar. 4, 1957, Ser. No.643,781 14 Claims. (Cl. 250-108) This invention relates to radiationinstruments and particularly to teletherapy heads wherein a radioactivesource, such as cobalt 60, which is dangerous when exposed, must bemoved from a safety position deep within the shielding of the head to aradiation position adjacent an aperture, to permit the emanation ofradiation for a limited time only; and must then promptly and securelybe restored to the safety position.

The purposes of the present invention include: providing such aradiation instrument, and particularly a teletherapy head, with aneasily moved source-carrier of minimum mass, nevertheless assuring themaximum of shielding whether the source is in safety position or inradiation position or being moved therebetween; assuring accurateregistration of the radioactive source with the radiation aperture;providing a fail-safe control means for positioning the source and foremergency return of the source to the safety position; providing anarticulated carrier having a minimum of mechanical connector parts andarticulated in such manner as to achieve close fit of the parts withinthe head; using the articulated carrier to furnish shielding.

I attain these purposes, and others which will be apparent from thisspecification, in the manner set forth hereinafter and as shown in thedrawings, in which:

FIGURE 1 is a front elevation, somewhat schematic, of a teletherapy headembodying the present invention;

FIGURE 2 is an enlarged sectional view taken along line 2-2 of FIGURE 1,with the radioactive source in safety position;

FIGURE 3 is a sectional view similar to FIGURE 2, showing the sourcemoved to radiation position in registration with the radiation aperture;

FIGURE 4 is a side elevation of a typical link of the articulatedcarrier, with part of an adjacent link shown in phantom lines;

FIGURE 5 is an exploded view of two adjacent links, taken from the innerside of the curve of the head passage;

FIGURE 6 is a left end view of the link of FIGURE 4; and

FIGURE 7 is a right end view of the link of FIGURE 4.

The teletherapy head generally designated a in FIG- URE 1 comprises ahousing b which is nearly spherical in general contour, and is mountedon a lateral axis x for rotation on trunnion-like side extensions 0.Projecting from the housing b near its lower and forward portion is acollimator face d mounting a shield-holding ring e by which any one of avariety of spacers may be held to a collimator face. Such spacers (asthe plastic hollow cylindrical spacer f) fix the distance from thepatients body at which the source of radiation is to be used. At itsupper end the housing b has a planar face g which is utilized ashereinafter more fully set forth.

Within the housing b I locate at substantially its center athick-walled, hollow cylindrical safety-position shield 11. Within acollimator face aperture 12 of the housing b I locate a somewhatsimilar, though smaller, hollow cylindrical collimator face shield 13with its cylinder axis substantially perpendicular to the housing faced. The shields 11, 13 are preferably machined of a material havingexceptionally high shielding qualities, i.e., resistance to the passageof the emanations from radioactive sources.

3,032,661 Patented May I, 1962 Tungsten alloys have proved well-suitedfor this purpose. A plurality of tapered depressions 14 formed in theouter cylidrical surfaces of the shields 11, 13 are filled when a massof lead shielding 15 is cast within the housing b, holding these shieldspermanently in place.

Before casting the lead shielding in place, however, a tubular track 16,preferably circular in cross-section and having a bend portion 17 whosebend radius is roughly half the diameter of the head a, is affixed withits inner end 18 inside the safety position shield 11, with the axis ofthis cylindrical shield 11 directed perpendicular to the face g. Thetube axis of the track 16 lies entirely within a plane corresponding tothat shown in the sectional views FIGURES 2, 3.

The outer end of the tubular track 16 consists of a straight outer trackportion 19 parallel to the axis of the safety position shield 11, andwhere it joins the 180 bend portion it enters the head a through acasting outlet 20. Adjacent the inner end of the central opening in thecollimater face shield 13, the tubular track has, on the outer side ofits 180 bend portion 17, a radiation opening 21. Radiations emittedthrough this opening are controlled by the use of a collimator plughaving a suitable inner contour. One of such plugs, numbered 22 andhaving a truncated conical aperture, is shown fitted within thecylindrical collimator face shield 13. Such plugs all employ a similarradially enlarged outer retention portion 23, into which the plasticspacer f is engaged. Both are held within the shield-holding ring eunder the overhanging projecting ends 24 of twistable knobs 25, or byother suitable retention means.

A tubular insert 26, of slightly greater diameter than the innerdiameter of the safety shield 11, connects its bore to the face g.

The safety position for the radioactive source is at the center of thecylindrical shield 11. A tungsten alloy inner shielding plug 27 isremovably positioned and retained therein under a larger diameter leadplug 28 which removably fills the extension tube 26.

One of the principal problems met by the present invention is to movethe radioactive source from the safety po sition to the radiationposition in precise registration with the radiation opening 21 in thetrack 16 and the central aperture of the collimator plug 22;nevertheless, to provide adequate shielding between the safety positionand the radiation position when the source is removed from the radiationposition, and also to provide shielding between such source and thecasting outlet 20.

I utilize an articulated source-carrier generally designated 29, whichbears the radioactive source at its inner end, rides easily within thetrack 16, and is manipulated from its outer end by means outside of thehousing b and with complete safety to the operator. This articulatedsource-carrier is essentially a train of source-positioning links,hereinafter more fully described, the inner links of which serve asadditional shielding material for the source;

This train includes a radiation source link 30, located at the inner endof the carrier train and shown in FIG- -URE 2 in the safety position andin FIGURE 3 in the radiation position. A radio-active source 31, such ascobalt 60, is loaded within a lateral, threaded bore 32 in the sourcelink 30. The link 30 is substantially cylindrical in shape, its outerdiameter being sufficiently less than the inner diameter of the tubulartrack 16 to slide readily within the 180 bend portion 17. Angularregistration within the plane shown in cross-section, FIGURES 2 and 3,is obtained by connecting the successive links to each other in a manneras will avoid twisting. As between the source link 30 and the outwardlyadjacent link to which it is coupled (hereinafter referred to as thecoupling link 33) this result is obtained by means of a removablecoupling pin 34, arranged perpendicular to the plane of 3 the 180 bendin the track 16, through a tongue portion 35 of the source link 30 and amating groove portion 36 at the adjacent end of the coupling link 33.These tongue-and-groove portions serve to continue the shieldingmaterial with minimum interruption.

Articulation of the links, despite their tongue-andgroove end portions,is achieved as follows: Within the plane shown in FIGURES 2 and 3 thelink portions on the inward side of the curved track 16 are consideredthe inner portions. Outward of the centerline of the links, thetongue-and-groove portions described are formed perpendicularly to theaxes of the links; but inwardly of their centerlines one or the other ofthem (here the tongue portion 35 of the source link 30) is cut away at arelief angle sufficient to permit relative slant of adjacent links, sothe articulated carrier may pass around the 180 bend. Inasmuch as thisbend is formed to a circular arc, the relief angle to be provided may bereadily computed by dividing 180 by the number of links necessary tofill the path within the bend. For instance, if ten links are necessaryto fill this path, the minimum relief angle to be cut away at eachjuncture of adjacent links would be 18. In practice a slightly greaterangle should be provided.

Firmly secured by an end pin 37 within a blind centerline bore 38 withinthe coupling link 33, is the inner end of a control cable 39, upon whichall the remaining articulated links are stiung as hereinafter described.The centerline bore 33 in the coupling link is at its end opposite theattachment to the source link; this end includes a tongue portion 40,shown in section in the drawings, for mating with a groove portion ofthe next adjacent link, hereinafter to be described, but they are notpinned together.

Intermediate the coupling link 33 and the outermost trigger link 41, allthe intermediate links are identical in size and shape to those shown inFIGURES 4, 5, 6 and 7, inclusive, but are of two different materials.The five links starting adjacent the coupling link 33 and extendingoutwardly therefrom are referred to as the shielding links 42; these areformed of a tungsten alloy having high shielding qualities. The sixlinks next adjacent are identified as the low mass links 43; these areformed of any substantially rigid light-weight material, such as nylonplastic, which may be held to sufficiently close tolerance to avoid anytwisting in the mating tongue-and-groove connecting portions.

Referring to FIGURES 4 to 7, inclusive, each of the shielding links 42and low mass links 43 is generally cylindrical and has at one end asquare-cut groove 44, formed perpendicular to the cylinder axis, and atthe other end a projecting tongue including a tongue portion 45 formedto mate within such a square-cut groove and having at the inner side ofthe curve an angularly cut-back tongue portion 46, together with faceswhich flank the tongue base, formed at the relief angle or bevel-say 18.The grooves 44 receive the tongue portions 45, 46 with close tolerance,so that the links need not be pinned as long as they are not permittedto spread apart from each other. When the source is in safety position,shielding material is provided by the shielding links 42 between thesafety position and the radiation position; similarly, when the sourceis in radiation position, they provide shieldingbetween the radiationposition and the casting outlet. The low mass links are, in either case,positioned where no additional shielding is necessary; therefore, theirlight-weight construction minimizes the mass to be moved.

Each of the shielding links 42 and low mass links 43 has a centerlinebore 47 including taperingly enlarged end portions 48 of sufficientdepth and taper to permit the control cable 39 to assume either curvedor straight alignment without loosening or otherwise aifecting thespacing between adjacent links. Thus the links have a snakelike freedomto bend in the plane which is defined by the mating tongue-and-grooveportions 44, 45, 46, to coincide with the plane of the track 16 and toassure positioning of the source in perfect registration with theradiation opening 21.

The trigger link 41 is the outermost link of the articulatedsource-carrier. Its innermost end is grooved at 44, to mate with thetongue of the adjacent low mass link. It has a similar flared-endcenterline bore 47, and its outer diameter is the same as the otherlinks which make up the carrier. Pin-pointed within a recess 49 in theouter side of the link is a trigger-shaped finger grip projection 50which extends outwardly through an elongated slot 51 in the outer sideof the outer track portion 19. This finger grip projection 50 is free todeflect upward and inward as shown in the dashed lines of FIGURE 1,against a stop pin 52; thus chance contact with the projection will nottend to move the radioactive source out of the safety position shown inFIGURE 2. However, the projection 50 is readily grasped for moving thesource from the radiation position of FIGURE 3 toward the safetyposition and when pressed in this direction will not deflect out of theway. Thus while the link 41 is referred to as a trigger link, the termis descriptive of its appearance; other finger grip projections wouldserve the same function.

' The outermost end of the trigger link 41 has a concave face 53 againstwhich seats a convex-ended plug 54 having a centerline bore 55 throughwhich the control cable 39 passes, and an assembly set-screw 56extending inward from the outer side and adapted to be tightened againstthe control cable. This assembly set-screw 56 is used only duringassembly, installation and dis-assembly of the articulatedsource-carrier 29, not during normal use. Once installation is complete,the assembly set-screw 56 is backed ofi, so that the matingtongue-and-groove portions of the links of the source-carrier 29 may becontinuously held pressed together, as herein set out, and the cable 39held continuously in tension.

Opposite the convex end of the plug 54, its diameter is reduced toprovide an annular seating flange 54 for the inner end of a coiledcompression spring 58, whose outer end bears against a similar seatingflange formed on a centrally bored closing plug 59 retained by aset-screw 60 in the outer end of the tubular track 16. The control cablepasses freely through the centerbore of the closing plug 59 and issecured around a rotatable drum 61 on the shaft of an electric torquemotor 62 mounted to the face plate g. The compression spring 58, actingagainst the closing plug 59, holds the cable 39 under continuous tension(and the links strung thereon aligned under continuous compression)exerted all the way to the coupling link 33.

The motor 62 preferably includes a preset torque clutch or other meansto permit the'drum 61 to stop when subjected to a preselected amount oftorque exerted in the control cable 39 when the radioactive source is inthe radiation position heretofore described. Such torque may be broughtabout in a variety of ways. In the drawing, FIGURE 3, it is shown asbeing induced by compressing the spring 58 to its fiat height; but otherways may be preferred.

When the motor 62 is energized by a power source, not shown, to exerttension on the control cable, the radioactive source 31 will be drawnfrom the safety position shown in FIGURE 2 to the radiation positionshown in FIGURE 3, that is, opposite the radiation aperture. When themotor is turned 01f, or should the power source fail, the torque exertedby the motor will cease, and the compression spring will cause animmediate return of the radioactive source 31 to within the safetyposition cylindrical shield 11. To avoid any abrupt force, the shieldingplug 27 is provided with a nylon or other plastic bumper 63.

The articulated sourcecarrier herein described thus permits the safepositioning, from the remote outer end of the carrier, of a radioactivesource which would be dangerous were there any gap in the shielding.Although the source-carrier possesses snake-like flexibility in theplane of its mating tongue-and-groove juncture portions, whichcorresponds to the plane of the 180 bend in the tubular track 16, itsprecisely controlled length and inability to twist achieve preciseregistration at the radiation aperture, so that there will be noquestion as to the strength of the radiations emanating through thecollimator plug 22. Thus the source-carrier is readily manipulated fromits end remote in distance from the source and removed from it by asubstantial angular bend.

A plurality of studs 64 projecting from the face plate g of the head amay be used to mount a safe for changing the radioactive source fromtime to time. This is done by disconnecting the cable 39 from the drum6]., and re moving the pin which mounts the finger grip projection 50,thus permitting the articulated source-carrier to be moved furtherinward when the shielding plug 27 and its associated lead plug arewithdrawn outwardly through an opening in the face plate g. These plugsmay be safely removed in a variety of ways, which are known in the art,as for example, into one aperture of an indexable turret in a safe. Thecoupling pin 34 may then be removed by conventional means, such as aremote-controlled screwdriver, to permit the source link 30 to bedisconnected and received in another aperture of such a rotating turret,and a substitute source link may be indexed in place and secured byre-engaging the coupling pin 34.

In contrast to teletherapy heads now in use, the head shown and hereindescribed provides a minimum mass source-carrier with a maximum ofshielding. The minimmum mass permits the operation and control by arelatively small motor '62. Such motor may be fitted with a variety oflimit switches or other means by which the positioning of the source maybe controlled.

Extensive changes of details may be made without departing from thescope of this invention. For example, the links might be enlarged to asomewhat barrel-shaped contour at their centers if this were necessaryfor easier movement within the tubular track and even more completeshielding. Other cross-sections of track might be used, with thecross-sectional shape of the links modified for easy sliding fittherein.

The tongue-and-groove link-joining means shown, including the holding ofthe links together by the compression spring 58, provides the maximumshielding with a minimum of mechanical complexity, easy manufacture, andfreedom from a plurality of mechanical connectors which conceivablymight become disengaged and jam within the track 16. The tension-heldcable cannot kink out of its path; the compression spring which suppliesthe tension also assures fail-safe operation. Other articulatedlink-joining details might be substituted, relative angular movement inthe plane of curvature of the path being pro vided and twist out of suchplane being restrained.

Many such modifications and others will occur to those skilled in theart. Accordingly, this invention is not to be construed narrowly, butinstead as fully coextensive with the scope of the claims which follow.

I claim:

1. A teletherapy head comprising a mass of shielding material ofgenerally spherical configuration and a curved hollow tubular trackembedded therein, the track having a safety position locatedsubstantially at the center of the mass, an outlet to the outer side ofthe head, and a radio-: active radiation position intermediate thesafety position and the outlet, the head having a radioactive radiationaperture adjacent the radiation position of the track, together with anarticulated source-carrier having at its inner end a source link, andhaving links outwardly thereadjacent formed of shielding material andsubstantially filling the inner cross-sectional area of the tubulartrack, together further with position-control means at the outletincluding a tension connector, a motor operatively connected therewithto apply tension thereto, whereby to move the source from the safetyposition to the radiation position, and an 6 opposing compression springurging the source-carrier toward the safety position.

2. In a radiation instrument having an innermost storage position for aradioactive source and a radiation position somewhat outward therefrom,the combination comprising a shielded head having a walled passagecurved 'in a plane and connecting the storage position, the radiationposition, and a positioning control point outside the head, togetherwith articulated rigid source-positioning links movable within saidpassage and carrying the source at their inner end, at least some of theinner links being of radioactive shielding material, a tension connectorconnecting said source-positioning links to said positioning controlpoint and a compression spring urging the sourcepositioning links towardstorage position, together further with means for exerting tension onsaid tension connector at said positioning control point in oppositionto said spring whereby to draw the source-positioning links to saidradiation position.

3. The combination as defined in claim 2, the walled passage having alongitudinal slot whose length at least equals the distance of movementwithin said passage of said articulated source-positioning links, one ofsaid links located remote from the source having a finger gripprojection extending through said slot.

4. For use within a teletherapy head having within it a curved tubulartrack including a shielded safety position, a radiation apertureposition, and an outlet from the head, an articulatedradiation-shielding carrier for a radioactive source including a sourcelink remote from the outlet, a plurality of links formed of radioactiveradiation-shielding material and having a cross-sectional shape smallerthan and conforming substantially to the inner cross-section of thetubular track, whereby to fit slidingly therein, together withmanipulative means at the carrier end remote from the source linkwhereby to position the source link along the track selectively in theradiation position and to return it to safety position.

5. A shielded teletherapy head for containing a source of radioactiveradiation and having within it a storage position for the source, aradiation position therefor, a radiation aperture adjacent saidradiation position, and a tunnel-like passage extending from the storageposition to and beyond the radiation position, together with asource-holding member and a train of links secured thereto andaccommodated and movable within said passage, the links having suchcross-section as to fit slidingly within and substantially to fill thepassage thereof, said links adjacent said source-holding member andextending for a length substantially as great as that from the storageposition to the radiation position, being formed of radiation-shieldingmaterial, together with means for moving said train of links withn saidpassage whereby to postion the source selectively in radiation positionand in storage position.

6. The combination comprising a shielded head having a storage positionfor a radioactive source, a radiation position therefor, a radiationaperture thereadjacent, and a curved tunnel-like passage extending fromthe storage position beyond the radiation position, and having an outletfrom the head, together with a source-positioning train movable withinsaid passage and including an articulated carrier having asource-holding member and a plurality of articulated shielding linksadjacent said member and extending therefrom outwardly along saidpassage a distance substantially as great as the distance from thestorage position to the radiation position, said carrier further havingadditional articulated links extending along the passage a distance asgreat as that from the outlet to the outermost shielding link, measuredwhen the sourceholding member is in the storage position.

7. The combination defined in claim 6, said additional articulated linksbeing formed of light-Weight non-shielding material whereby to lessenthe mass of the carrier.

8. In a shielded teletherapy head having a tunnel-like source-trackcurved in a plane, said track including a storage position near thecenter of the head and a radiation position outward therefrom,source-positioning means comprising a plurality of links including aninnermost source-holding link within such tunnel-like track and.articulated link-joining means permitting said links relative angularmovement in the plane of said curved path and restraining them againstrelative twist, at least some of the links near said source-holding linkbeing of radioactive shielding material.

9. Source-positioning means as defined in claim 8, the link-joiningmechanism including mating tongue-andgroove portions formed in the planeof curvature of the passage and cut away inward of the center of thepath.

10. Articulated source-positioning means for a teletherapy head having aplanar source passage including a curved portion extending from insideto outside the head, comprising a plurality of unpinned links eachhaving a centerline bore and having mating tongue-and-groove endportions, the parts of said tongue-and-groove portions on the outer sideof the curve being formed perpendicular to the centerline bore, one partthereof at each tongueand-groove junction including an angle less than90, together with a flexible cable extending from the innermost unpinnedlink through the centerline bores of said links to and through theoutermost link, and retention means secured to the cable outward of theoutermost link for retaining said tongue-and-groove portions of adjacentlinks in registration with each other, a plurality of said links beingformed of radioactive shielding material.

11. For use in a radiation instrument having a curved passage for movinga source of radioactive radiation from a safety position to a radiationaperture, an articulated radiation-shielding source-carrier including asource-holding link substantially at one end thereof, a plurality ofarticulated links formed of radiation-shielding material and of suchcross-sectional area and shape as to substantially fill and fitslidingly within such curved passage, together with manipulative meansat the other end whereby to move the source-carrying link along thepassage from the safety position to the radiation aperture and back.

12. For moving a source of radioactive radiation within a curvedtunnel-like passage of a teletherapy head from storage position to aradiation position and back, a lightweight shielding carrier for aradioactive source comprising a source-holding member and a plurality ofarticulated links operatively connected thereto and to each other, saidcarrier being such length as to extend from the storage position beyondthe radiation position to the outer side of the head, the links adjacentthe source-holding member being formed of radiation-shielding material,the links remote from the source-holding member being formed oflightweight material whereby the total mass of the carrier is lessened.

13. Means for moving a source of radioactive radiation within ateletherapy head along a tunnel-like path having a curved path portion,comprising a flexible cable secured at its inner end to such radiationsource and at its outer end to a tension-applying control means, aplurality of shielding links riding within such tunnel-like path atleast the length of the curved portion thereof and strung beadlike alongsaid cable outward of said source, and a spring yieldably exertingcompression inwardly against said links whereby to hold the cablecontinuously in tension around .the curved portion of such path.

14. Fail-safe means for moving a source of radioactive radiation withina teletherapy head along a tunnel-like path having a curved portion,comprising the mechanism defined in claim 13, the spring being helicaland surrounding a portion of the cable adjacent the outer end of saidlinks so strung, the outer end of the spring bearing against a fixedmember having an aperture through which the outer cable end passes,whereby to move the source inwardly away from the fixed member toward asafety position in case of failure of the tension-applying controlmeans.

References Cited in the file of this patent UNITED STATES PATENTS2,477,648 Piggot Aug. 2, 1949 2,551,491 Gilks May 1, 1951 2,670,443Pennock et al. Feb. 23, 1953 2,711,485 Pennock et al. June 21, 19552,750,517 Baum June 12, 1956 2,772,361 Hiestand Nov. 27, 1956 2,798,164Untermyer July 2, 1957 2,821,636 Jefferson Jan. 28, 1958 2,843,754Coestello July 15, 1958 2,844,736 Johns July 22, 1958 2,849,621 ClarkAug. 26, 1958 2,862,108 Meilink Nov. 25, 1958 2,872,587 Stein Feb. 3,1959

